Accident Overview
On January 22, 2016, about 1530 central standard time, a Piper PA-31 airplane, registration N997DN, sustained substantial damage during a forced landing near Denton, Texas. The commercial-rated pilot received minor injuries. The flight was conducted under 14 CFR Part 91 without a flight plan in visual meteorological conditions. The local flight had departed Denton Enterprise Airport (KDTO) at about 1500.
Preflight and Fueling
The pilot reported that the accident flight was a routine maintenance flight following maintenance and a 2-year period of infrequent flying. Several days prior, the pilot conducted an extensive preflight and supervised fueling. The inboard tanks were filled to 56 gallons, outboard tanks had 10 gallons added, and nacelle tanks were empty. During a maintenance test run three days before the accident, the pilot started and shut down engines on inboard tanks, then taxied and ran engines on outboard tanks for about 30 minutes. During the preflight on the accident day, the pilot noted a fuel spot under the right main fuel tank sump; the plug was not seated correctly. He estimated less than a cup of fuel was lost. At takeoff, the pilot estimated 120 gallons of fuel on board, with no additional fuel added and no visual verification of fuel quantity since the run-up three days prior.
Flight and Engine Failure
Run-up revealed no anomalies. The pilot departed with fuel selected to inboard tanks, later switched to outboard at altitude. When the right engine fuel flow dropped, he switched back to inboard. He climbed to 1,000 feet, checked systems, conducted a low approach at Bishop Field, then climbed to 2,000 feet. While performing the cruise checklist, the right engine surged. The pilot noted behavior consistent with no fuel or fuel flow. He checked fuel selector valves and troubleshooted without resolution. He obtained clearance for a downwind leg to runway 36 at DTO, at which time the right engine lost power. Before he could declare an emergency and secure the right engine, the left engine surged and lost power. During the forced landing, both wings and engine nacelles were substantially damaged.
Post-Accident Examination
FAA responders smelled fuel at the scene but found no evidence of fuel. The fuel tanks were empty, with no pooling of fuel in the debris field or where the airplane came to rest. The airplane recovery team recovered only one quart of fuel from the left fuel tank. An examination of the airframe, wings, and fuel system—conducted with the NTSB investigator-in-charge, FAA inspectors, and a Piper investigator—revealed that the fuel tanks and fuel system had not been compromised during the accident. No mechanical anomalies were noted with the engine, airframe, or airframe fuel system that would have precluded normal operation.
Data Analysis
The airplane was equipped with a J.P. Instruments EDM-790 recorder that monitored and stored engine parameters. The unit contained 2.7 hours of data across 15 power cycles, capturing both the engine run (36 minutes) and the accident flight (30 minutes). Based on the operator's calibrations, total fuel consumption was 5.6 gallons for the engine run and 19.2 gallons for the accident flight. Performance data from the airplane flight manual indicate fuel consumption of 54 gph at high cruise and 28 gph at maximum endurance for both engines. Investigators estimated fuel burn for the maintenance test run (three days prior) at 10 to 18 gallons and for the accident flight at 27 to 50 gallons. Fuel receipts confirmed the addition of 99.36 gallons before the maintenance test run on January 18, 2016.